Solar Panel Instalation

Hadenough

Hadenough

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Just taken delivery of a 100w solar panel and will be fabricating the brackets this afternoon in the workshop at home. Being a bit of a big spanner man I'm not sure if I can test the output without wiring it through the regulator on the boat. Can I connect it up to a multi meter (set to amps I presume) and point it at the sun without doing any damage? :confused:
 
No you need a battery. You can measure the open circuit voltage if you want. Multimeter on volts the reading will be about 23v so set the multimeter to an appropriate scale.
 
noelex said:
No you need a battery. You can measure the open circuit voltage if you want. Multimeter on volts the reading will be about 23v so set the multimeter to an appropriate scale.
Click to expand...

Thanks. I've got a 12V - 90AH battery in the workshop so if I understand that's pos and neg from the panel to pos and neg on the battery and measure the volts across the battery pos and neg. Think I might wait till the sun is less bright and definitely not grab the bare ends! Don't want to end up like this :confused: Back to the fabricating, bet the sun doesn't shine like this when I actually need it onboard!!
 
If you have a battery you can measure the current, which with the voltage will give you the power the solar panel is putting out.
There is no need for a regulator if you connect it for a short time, but keep an eye on the voltage and don't go over 14.5 or so. The battery needs to be discharged or even better if can put a moderate load on it like a car headlamp.
To measure the current you have to connect the multimeter in series so the current goes through the meter. You need to plug the leads into the correct terminals on the multimeter. Finally check you multimeter can handle 10A most can for 30 seconds.

There is some risk of damaging the multimeter if you connect it up wrong. If you just want to see the solar panel working a safe test is to measure the voltage of the battery, then attach the solar panel the voltage sould rise. This will show the panel is working, but does not tell you how much it is putting out. For voltage the multimeter is connected in parallel.
Be careful around the battery when it's charging a spark can in rare cases cause an explosion wearing safety glasses is a very sensible precaution.
 
Hadenough said:
Thanks. I've got a 12V - 90AH battery in the workshop so if I understand that's pos and neg from the panel to pos and neg on the battery and measure the volts across the battery pos and neg. Think I might wait till the sun is less bright and definitely not grab the bare ends! Don't want to end up like this :confused: Back to the fabricating, bet the sun doesn't shine like this when I actually need it onboard!!
Click to expand...

Connect the panel to the battery as you say positive to positive, negative to negative and measure the volts. As the battery charges the volts should rise.

However not much of a test.

Connect an ammeter in series and you'll have some idea of the current.

Still not much of a test , at least if the battery is already charged

A 100watt panel should light a car head lamp bulb, but expose it progressively to the sun as without a controller it might blow the bulb.


Perhaps connect the bulb to the battery and then connect the panel via an ammeter. The ammeter will show the total of the current the bulb is taking plus what the battery is taking.


You'll not electrocute yourself with a 12 volt solar panel.

The hazards will be from the hot bulb and the remote risk of a spark at the battery terminals igniting any hydrogen there might be
 
markdj said:
I have measured the voltage from solar panels many times just by holding the multimeter to each wire with my fingers, there isn't any risk... Open circuit voltage will be about 20 volts DC depending on the type of panel.
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If the resistance across the terminals was low - say, hands wet with salt water - you might get a burn, rather than a shock. Not likely with a relatively low wattage like 100W, where the maximum current would be around 5-8 amps, but I've just had 2.2 KW put on the roof, and the maximum current out of that is something like 110-150 A depending on the output voltage. I don't fancy going near that without insulating gloves.
 
AntarcticPilot said:
If the resistance across the terminals was low - say, hands wet with salt water - you might get a burn, rather than a shock. Not likely with a relatively low wattage like 100W, where the maximum current would be around 5-8 amps, but I've just had 2.2 KW put on the roof, and the maximum current out of that is something like 110-150 A depending on the output voltage. I don't fancy going near that without insulating gloves.
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Surely 20 volts is safe enough even if the maximum current available was hundreds of amps. At that voltage the current passing though you will be too low to be harmfull wont it ?

Take for example a 24 volt DC system on a boat. It does not present an electrocution threat even though the battery could deliver several hundred amps does it.

What is the output voltage from your roof top array. If its 100 volts or more maybe a potential electrocution risk
 
Last edited:
vyv_cox said:
I believe the cutoff between 'safe' and 'hazardous' DC is 50 volts.
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An old saying:

It's the VOLTS wot jolts . . . It's the MILL's wot kills". :eek:

10mA through to body is considered fatal.

You won't get a burn or a shock from a single solar panel but you might get a burn if you short the output terminals together on a day like today and then try and hold the wires.
 
I happened to measure the outputs of my 5w Spectralite panel today just after noon.

Open circuit voltage was 19.2v. Closed circuit amps was 0.35A.
 
"I believe the cutoff between 'safe' and 'hazardous' DC is 50 volts."

When I used to design hand held machine control units we would limit the control voltage to 42 VAC as this was considered a "safe voltage"
 
Just connected the panel to a discharged battery - 11.8v. In this sun I got a steady rise to 12.8v off the battery over about 10 mins. Enough to tell me it's working. I'll leave the amps till I connect to my regulator which has a digital read out. Many thanks everyone.
 
Hadenough said:
Just connected the panel to a discharged battery - 11.8v. In this sun I got a steady rise to 12.8v off the battery over about 10 mins. Enough to tell me it's working. I'll leave the amps till I connect to my regulator which has a digital read out. Many thanks everyone.
Click to expand...

The panel is working just as it should do for that test. I think you are wise to leave a more detailed test of output until its fully installed. Many of the regulator displays are a bit optimistic, take this into account when looking at the output on the display. Even better measure it with a clamp on multimeter ( every boat should have one) so you know what the error is.
 
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